Display the American flag
Old Glory is the natural symbol for showing your pride in American traditions. If you don't own a flag, FlagLine.com offers good products and service at good prices.
The Stars and Stripes can be displayed on more than just a flag pole. How about a shirt or hat? Maybe a coffee mug or tote bag? Here are good quality items from CafePress with the American flag, the "Betsy Ross" 13-star flag, and the "Don't Tread on Me" Gadsden flag.)
GoCollect has a selection of Independence Day collectibles you might want to browse. Some of this might be too cute for you (e.g., "bearyproud" teddy bears), but there are some interesting items here for just about any taste.
If you would like something more artistic, consider Jasper Johns' Three Flags or another patriotic art print.